The invention relates to industrial internal combustion engines, and more particularly to a governing system for holding the engine at constant speed.
The invention has application to various industrial internal combustion engines, including natural gas engines, diesel engines, gas turbine engines, etc. In one desirable application, the invention is used with an industrial internal combustion engine used to drive an electrical power generator for a utility, factory, or the like, preferably matching a desired frequency such as 60 Hz in the United States or 50 Hz in Europe, notwithstanding load changes. The invention has other applications where it is desired to hold the engine at some constant speed.
Industrial internal combustion engines use governors to hold the engine at a constant speed. A feedback system responds to the engine and supplies a feedback signal to the governor which compares observed speed against desired speed to generate a delta or error signal which is supplied to the engine throttle to correctively increase or decrease engine speed in an attempt to drive the delta or error signal to zero. Natural gas engines have poorer load response than diesel engines so that a large load placed on a natural gas engine may stall the engine or may result in an unacceptably low dip in engine speed. Response time is particularly important when the driven load is an electrical generator when isolated from the electric utility grid. In these applications, it is important to minimize the magnitude and duration of excursion from synchronous frequency. Relying only upon feedback necessarily requires delay because the engine speed change must first be sensed before it can be corrected.
A feedforward system provides quicker response, and can be used to anticipate engine speed changes. It is known in the prior art to sense load changes and then send an anticipation signal to the engine control unit to change throttle position before the feedback system senses a speed change. This reduces frequency excursions caused by load transients. This type of feedforward system based on load sensing to provide an anticipation signal is disclosed in xe2x80x9cLoad Pulse Unitxe2x80x9d, Woodward Product Specification 82388C, 1998.
In another feedforward system, load anticipation trim signals are provided as feedforward signals which anticipate engine response to changes in commanded engine loading. The feedforward signals are summed with the feedback system error signal to control the throttle, for which further reference may be had to Thomberg et al U.S. Pat. No. 5,429,089, incorporated herein by reference.
In another feedforward system, engine output power is allowed to rise in anticipation of increased load. In response to a load command, a small delta speed change is applied to the engine over a time interval from when the load command is first sensed. This type of feedforward system is desirable when the amount of extra torque required is not known.
The present invention provides a governing system for an industrial internal combustion engine and relies upon predictively anticipating load change to maintain constant engine speed notwithstanding load changes. The amount of extra required torque is known ahead of time, at least approximately, and precise control is initiated before the extra load is actually applied. In a preferred embodiment, the invention is applicable in a PID, proportional integral differential or derivative, control loop to directly set the integral term with an update applied only once, without re-application.